Noble gas signatures of magmatic sources and processes.

Abstract

The degree of partial melting affects the concentration of noble gases in a lava. However, this effect is apparent only for heavier noble gases (Ar, Kr, Xe), in the case of Loihi samples, because kinetic proc esses work more effectively for lighter noble gases (He, Ne). Further, the amounts of atmospheric Ar ob served in volcanic rocks are sometimes lower than those expected from the solubility data for Ar in the atmosphere at the surface. This suggests that the samples did not equilibrate with the atmospheric Ar, and the degassing of the magmatic Ar is incomplete. The 3He/4He-3He/36Ar diagram indicates that the 3He/36Ar ratios are quite variable even though the 'He/'He ratios are relatively uniform for MORBs and for some samples from hot spot areas. The higher 3He/36Ar ratios observed for dunites relative to olivine phenocrysts could be a result of secondary introduction of He into dunites from surrounding magma.

Irradiated interplanetary dust particles as a possible solution for the deuterium/hydrogen paradox of Earth's oceans

“…Searches in the Earth's crustal rocks also failed to find "missing" Xe. Kaneoka [1993] has shown that mantlederived rocks have higher Xe/Kr ratios than the atmosphere, implying that Earth's Xe may be trapped within the mantle. This could not account, however, for Xe that was brought in during the heavy bombardment period because that Xe would have been impact degassed directly into the atmosphere.…”

Magmatic processes revealed by noble gas signatures: the case of Unzen Volcano, Japan.

“…However, they have not been often used as tracers of mag matic processes and volcanic systems. Since it is expected that noble gas isotopes would be sensi tively affected by magmatic events, such as magma mixing and assimilation, they might have a po tential to contribute to volcanology (Hilton et al, 1993;Kaneoka, 1993;Marty et al, 1994). In this study, we have applied noble gas signatures to the magma of Unzen Volcano, Japan (Fig.…”